Initial provider implementation (#18)

This brings over the initial buildx prototype from pulumi/pulumi-docker
and fixes various build and release issues.

sdk/dotnet/Outputs/BuildContext.cs

@@ -0,0 +1,47 @@
+// *** WARNING: this file was generated by pulumi. ***
+// *** Do not edit by hand unless you're certain you know what you are doing! ***
+
+using System;
+using System.Collections.Generic;
+using System.Collections.Immutable;
+using System.Threading.Tasks;
+using Pulumi.Serialization;
+
+namespace Pulumi.DockerBuild.Outputs
+{
+
+    [OutputType]
+    public sealed class BuildContext
+    {
+        /// <summary>
+        /// Resources to use for build context.
+        /// 
+        /// The location can be:
+        /// * A relative or absolute path to a local directory (`.`, `./app`,
+        ///   `/app`, etc.).
+        /// * A remote URL of a Git repository, tarball, or plain text file
+        ///   (`https://github.com/user/myrepo.git`, `http://server/context.tar.gz`,
+        ///   etc.).
+        /// </summary>
+        public readonly string Location;
+        /// <summary>
+        /// Additional build contexts to use.
+        /// 
+        /// These contexts are accessed with `FROM name` or `--from=name`
+        /// statements when using Dockerfile 1.4+ syntax.
+        /// 
+        /// Values can be local paths, HTTP URLs, or  `docker-image://` images.
+        /// </summary>
+        public readonly ImmutableDictionary<string, Outputs.Context>? Named;
+
+        [OutputConstructor]
+        private BuildContext(
+            string location,
+
+            ImmutableDictionary<string, Outputs.Context>? named)
+        {
+            Location = location;
+            Named = named;
+        }
+    }
+}